Device for producing reduced porosity bone cement

Abstract

A mixing device for producing reduced porosity bone cement. The device having a movable member (6), preferably a movable piston, which is adapted to press out or discharge bone cement (2) from the mixing device (1). The piston is fixedly mounted in the mixing device. The piston maintains its position when bone cement (2) is mixed in a mixing space in the mixing device. The mixing device is under a vacuum during mixing. After mixing, the piston is released such that it can be drawn into the mixing device (1) toward a discharge opening (13) by a vacuum prevailing in the mixing device (1). The moving piston is used for collecting clumps of bone cement (2) in the mixing device (1) adjacent to the discharge opening (13). By collecting the clumps of bone cement by the moving piston (6) under a vacuum, the porosity of the bone cement (2) is reduced.

We claim: 
     
       1. A mixing device for producing reduced porosity bone cement, comprising: a mixing cylinder (3) having a mixing space, the mixing space having wall surfaces to which clumps of bone cement adhere during mixing of components of the bone cement;   means (4) for mixing the components in the mixing space,   a front member (5) provided at a front end of the mixing cylinder, the front member (5) having a discharge opening (13) for discharging bone cement from the mixing space,   a movable piston (6) fixably mounted at a rear end of the mixing cylinder, the movable piston being releasable from the rear end of the mixing cylinder and movable in the mixing space toward the discharge opening (13) for collecting the clumps of bone cement adjacent the discharge opening, and for discharging bone cement (2) through the discharge opening (13); and   a vacuum source (21) connected to the mixing device, generating a vacuum in the mixing space during mixing of the components;   wherein, when the movable piston (6) is released from the rear end of the mixing cylinder and moved in the mixing space for collecting the clumps of bone cement adjacent to the discharge opening (13) such that the vacuum generated in the mixing space by the vacuum source generates a vacuum in pores formed in the bone cement (2) during the collecting of the clumps of bone cement, whereby the size of the pores is reduced when the bone cement (2), after collecting, is exposed to atmospheric pressure; and   wherein the vacuum source (21) is connected to the front member (5).   
     
     
       2. A mixing device according to claim 1, wherein the movable piston (6) is moved in the mixing space toward the discharge opening (13) by the vacuum generated by the vacuum source (21). 
     
     
       3. A mixing device according to claim 1, wherein the movable piston (6) comprises at least one gripping portion (30) and the mixing cylinder comprises at least one corresponding gripping portion (28), the gripping portions (28, 30) of the movable piston (6) and the mixing cylinder are engaged with each other for fixing the movable piston (6) to the mixing cylinder, and the gripping portions (28, 30) are disengaged from each other by at least one of: rotating the movable piston (6) relative to the mixing cylinder and rotating the mixing cylinder relative to the movable piston (6). 
     
     
       4. A mixing device according to claim 3, wherein the gripping portions (28, 30) are disengaged from each other by rotating the mixing cylinder relative to the movable piston (6) after the movable piston (6) is placed into engagement with a separate member (34), the separate member prevents the movable piston (6) from rotating when the mixing cylinder is rotated relative to the separate member (34). 
     
     
       5. A mixing device according to claim 1, wherein the front member (5) is a cap adapted to seal the mixing space at the front end of the mixing cylinder, and an aperture (10) for the mixing means (4) is provided in the cap; the discharge opening has a connecting-pipe section (19); and a hose (20) extending from the vacuum source (21) is connected to the connecting-pipe section (19). 
     
     
       6. A mixing device according to claim 5, wherein the connecting-pipe section (19) forms a part of a plug (15) which is located in a tube section (12) provided on the cap. 
     
     
       7. A mixing device according to claim 6, wherein the tube section (12) is provided with external threads (14), and the plug (15) has a flange (17) with internal threads (18) for engagement with the external threads (14). 
     
     
       8. A mixing device according to claim 1, wherein a discharge pipe (16) for discharging bone cement from the mixing space is provided on a tube section (12) formed on the front member (5). 
     
     
       9. A mixing device according to claim 8, wherein the discharge pipe (16) is provided with internal threads (27) for engagement with external threads (14) provided on the tube section (12).